1. Field of the Invention
The present invention relates to a liquid cooling type cathode-ray tube for a projector.
2. Description of the Related Art
Such a video projector has been known in which single-color cathode-ray tubes of red (R), green (G) and blue (B) are arranged in line and a projection lens located on the front surface of each of the single-color cathode-ray tubes focuses an image on a screen.
FIG. 1 shows a typical liquid cooling type cathode-ray tube for a projection which is used in a video projector.
This liquid cooling type cathode-ray tube 1 is constructed in such a manner that a coupler 3, which will become a cooling liquid sealing member, is mounted on the side of a panel front surface 2a of a single-color cathode-ray tube body 2, a final lens 5 of a projection lens system is mounted on an opening portion 4 of the coupler 3 opposing to the panel front surface 2a and a cooling liquid 6 is filled into the space surrounded by the panel front surface 2a of the single color cathode-ray tube body 2, the coupler 3 and the final lens 5.
The coupler 3 is fixed to the cathode-ray tube body 2 through a packing 7 by means of a fixing spring 8 so as to be tightly contacted on the panel front surface 2a.
The final lens 5 is fixed to the coupler 3 by a lens fixing plate 10 through a packing 9 so as to be tightly in contact with the coupler 3.
The coupler 3 has a liquid fill hole 12 on the side surface thereof in the direction perpendicularly to this side surface, and through the liquid fill hole 12, the cooling liquid 6 is filled into and fills the coupler 3.
The liquid fill hole 12 is formed with a screw (female screw) on the inner surface thereof and is sealed through an O-ring as a sealing member by a sealing screw 13 after the cooling liquid 6 is filled thereinto through the liquid fill hole 12.
On the side surface of the coupler 3 opposite to the liquid fill hole 12, a pressure regulating valve or bellofram 15 for regulating the pressure of the cooling liquid 6 is provided. This diaphragm 15 is held by a diaphragm holder 16. This diaphragm 15 may be made of a membrane which is made of, for example, ethylene-propylene rubber, a mixture of ethylenepropylene rubber and silicone, or butyl-rubber. The diaphragm 15 takes an equilibrium state, a state swelling to the open air and a state contracted towards the cooling liquid depending on the volume change of the cooling liquid 6 due to the temperature change. By this, the pressure regulation of the cooling liquid 6 is achieved.
The coupler 3 has a box portion 3A whose side in contact with the front surface 2a of the cathode-ray tube body 2 is opened and a flange portion 3B formed on the open end portion 32 thereof, which are formed integrally, as shown in FIG. 2 (a perspective view of the coupler 3 as seen from the front side thereof), FIG. 3 (a perspective view of the coupler 3 as seen by rotating FIG. 2 by 180 degree) and FIG. 4 (a perspective view of the coupler 3 as seen from the rear side thereof). The box portion 3A is formed with an opening portion 4 formed on its front surface 18 for mounting the final lens 5, a mounting bore 19 on one side surface of the box portion 3A for mounting the diaphragm 15 and the liquid fill hole 12 on the opposite side surface of the bore 19 which liquid fill hole 12 has the female screw on its inner surface. At four places on the rear surface of the flange portion 3B, formed integrally with the flange portion 3B are legs 20 (20A,20B,20C,20D), each having a threaded hole 20a on its tip end for mounting the coupler 3 to the cathode-ray tube body 2.
By the way, in the case of the above described coupler 3, the holes used for mounting other parts thereon are formed in two axial directions. That is, as shown in FIG. 2 to FIG. 4, the threaded holes 22 on the front surface 18 of the box portion 3A for mounting the lens fixing plate 10 and the through holes 23 of the flange portion 3B are formed in one axis direction Z (direction along the tubular axis of the cathode-ray tube 2 in FIG. 1), while the threaded holes 24 for fixing the diaphragm cover and the liquid fill hole (threaded bore) 12 are formed in the other axis direction Y perpendicular to the one axis Z.
Accordingly, at the time of assembly using such a coupler 3, since the screw tightening process is performed in four directions, or the front and rear sides and the right and left sides of the coupler 3, the assembly process becomes complicated.
On the other hand, if the coupler 3 having such threaded holes 22, 24, 12 and through holes 23 in the two axis directions is made by a die-casting method, as shown in FIG. 5, a metal mold 31 used therefor is formed of a fixed mold 32, a movable mold 33 and in addition thereto two inserts 34, 35. The metal mold 31 is opened by moving the movable mold 33 in an arrow direction a and the inserts 34, 35 in arrow directions b, c perpendicular to the arrow direction a (see FIG. 6), and is closed by moving the same in the inverse directions.
Such a metal mold 31 needs a complicated structure of metal mold because the inserts 34,35 should be operated by a slide mechanism which is provided separate from the opening and closing operation of the movable mold 33. Therefore, the cost of the metal mold increases and the durability thereof deteriorates. As a result, the cost of the molded coupler increases. Generally, although trimming precess and threading process are performed after metal mold molding (so-called casting) process, the machine for carrying out these processes should have a multi-axis mechanism, which causes a high manufacturing cost.